JPH05345181A - Method and apparatus for setting exchange rate of reverse osmosis membrane - Google Patents

Abstract

PURPOSE:To attempt to make exchange rate of a membrane proper assuming that a guaranteed quality of water is ensured in the operation of a reverse osmosis type sea water desalination apparatus. CONSTITUTION:Electrical conductivity of permeated water through a unit reverse osmosis membrane 1F is measured by means of a conductivity meter on an instrument rack through a sampling rack 101 and it is input into a personal computer control apparatus 107 by means of a field operation panel 105. Operating condition of a plant is also input and the electric conductivity is corrected to obtain individual data and an average value and a standard deviation of these data. Pressure densifying factor and membrane deterioration rate factor are obtd. from these data and the membrane exchange rate is obtd. in such a way that the estimated quality of water after exchanging of the membrane does not violate a guaranteed value as the time elapses assuming that exchanging of the membrane is performed at a specified rate every year. Therefore, a proper exchange rate of the membrane can efficiently be set on every reverse osmosis membrane type sea water desalination apparatus and exchanging of the membrane can reasonably be performed and decrease in expenditure of maintenance and control is attainable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a large number of unit reverse osmosis membranes arranged in parallel or in series so as to pass feed water having high conductivity through the reverse osmosis membrane to form permeate having low conductivity. The present invention relates to a reverse osmosis membrane exchange rate setting method and apparatus used in a fresh water producing apparatus.

[0002]

2. Description of the Related Art In a fresh water producing apparatus constructed by connecting a number of unit reverse osmosis membranes in parallel or in series, the performance of the reverse osmosis membrane deteriorates with time. Require regular membrane replacement. This membrane exchange rate can be obtained from the membrane deterioration rate coefficient and the initial performance, but is usually determined by the membrane manufacturer. In the past, in actual membrane exchange, the membrane exchange rate specified by the membrane manufacturer was used, or the membrane exchange rate was individually used for each device by using a rough and poor basis.

However, the numerical value of the film manufacturer has been generalized so that it can be applied to any plant, so that the numerical value is high in safety and excessive. If the membrane exchange rate is too large, even the membrane having a remaining life is discarded, and the membrane is expensive, so that not only the maintenance cost becomes huge but also the resource is wasted. Therefore, particularly in medium-scale and large-scale equipment, the increase in maintenance cost due to the excessive membrane exchange rate poses a problem. On the other hand, the use of a poorly-valued value as the membrane exchange rate causes a problem that the device performance cannot be maintained when the value is lower than the appropriate value. Further, conventionally, there is also a case where a method of evaluating the membrane exchange rate by the overall performance of the apparatus is used, but in such a method, the exchanged membrane performance affects the overall performance of the plant, and the evaluation gradually becomes inaccurate. There is a problem of becoming a thing.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems in the prior art and to provide a reverse osmosis membrane exchange rate setting method and device capable of setting an appropriate membrane exchange rate. To do.

[0005]

In order to solve the above-mentioned problems, the present invention is used in a fresh water producing apparatus in which a large number of unit reverse osmosis membranes are provided in parallel or in series to constitute an aggregate. In the reverse osmosis membrane exchange rate setting method, the conductivity of permeated water is measured for each of the unit reverse osmosis membranes, the conductivity and the period of use of the unit reverse osmosis membrane are input to the processing means, and the input data is reversed. The deterioration rate coefficient of the reverse osmosis membrane is determined by the consolidation coefficient by which the osmosis membrane is consolidated, and the water quality of the permeated water predicted as the fresh water producing apparatus is always a predetermined value by the consolidation coefficient and the degradation rate coefficient. The membrane exchange rate, which is the ratio of the number of unit reverse osmosis membranes to be exchanged with respect to the total number of reverse osmosis membranes constituting the fresh water producing apparatus, is determined so as not to exceed
According to a second aspect of the present invention, in the reverse osmosis membrane exchange rate setting device for use in a fresh water producing apparatus, which is configured as an aggregate by providing a large number of unit reverse osmosis membranes in parallel or in series, To the processing means, the conductivity measuring means for measuring the conductivity of the permeated water, the input means for inputting the measured conductivity and the period of use of the unit reverse osmosis membrane, and the input data and the reverse osmosis membrane are consolidated. The processing means for determining the deterioration rate coefficient of the reverse osmosis membrane by the consolidation coefficient and the water quality of the permeate water predicted as the fresh water production apparatus calculated by the consolidation coefficient and the degradation rate coefficient is always Membrane exchange rate calculation means for determining the membrane exchange rate which is the ratio of the number of unit reverse osmosis membranes to be exchanged with respect to the total number of reverse osmosis membranes constituting the fresh water producing apparatus so as not to exceed a predetermined value. It is characterized by having.

[0006]

According to the invention of claim 1 or 2, because of the above-mentioned structure, the following operation occurs. First, the conductivity of permeated water is measured for each unit reverse osmosis membrane. In this case, the conductivity measuring means may be a device that automatically measures periodically, or a device that sequentially or individually measures by human operation. The measured conductivity and the duration of use of the membrane are then input into the processing means, where these data are processed. At this time, in order to locate these data, the measured unit reverse osmosis membrane name is also input. In this case, the input means may be of a form in which a person inputs each measured value together with its usage period or the reverse osmosis membrane use start time in advance and together with the measurement date. Alternatively, it may be an automatic input means. In the processing means, the film deterioration rate coefficient is calculated, but for the calculation, it is desirable to make statistically processed data of the input group of measured values. Since this data is used to accurately predict water quality in consideration of safety when finally calculating the membrane exchange rate, it is called, for example, the maximum value, minimum value, average value, or standard deviation. The value obtained by adding a multiple of the standard deviation to the average value, the maximum value or the like can be used for the subsequent calculation. On the other hand, when the reverse osmosis membrane is used under high pressure, it generally becomes compacted in accordance with its use time, the salt permeability is reduced, and the conductivity of the passing water is lowered. As the consolidation coefficient, which is an index of such decrease in salt permeability, for example, a value recommended by the film manufacturer is used, and this value is manually input to the processing means. This can correct the influence of the consolidation of the reverse osmosis membrane on the conductivity of the permeated water. However, a compaction coefficient input means is provided, and the recommended value or a table or curve of the compaction coefficient for the membrane use period obtained in advance by experiments etc. is input to the processing means, and the value is calculated from the membrane use period. Such a method may be used.
In this case, the membrane use period may be directly input by the input means, or the reverse osmosis membrane exchange date may be input in advance so that the membrane use period is calculated from the measurement time. Good. In the processing means, by further incorporating a relational expression between the film use period and the film deterioration rate coefficient,
The film deterioration rate coefficient is calculated from the consolidation coefficient, the input data, and the film usage period. The calculation of the membrane deterioration rate coefficient may be performed for each unit reverse osmosis membrane, but from the viewpoint of the capacity of the processing means, the measured group of data is statistically processed into one data as described above, It is preferable to use a group of reverse osmosis membranes as a unit. It should be noted that at a stage where the amount of accumulated data is small, a constant numerical value initially given as the film performance may be used. And finally, by the membrane exchange rate calculation means, from the compaction coefficient and the membrane deterioration rate coefficient, the water quality after membrane exchange predicted as a fresh water production apparatus does not always exceed a predetermined value determined from the required performance of the apparatus. The membrane exchange rate can be calculated. The membrane deterioration rate coefficient used here is a value calculated for each unit reverse osmosis membrane or a value calculated from statistically processed data, but when the conductivity is measured a plurality of times before water quality prediction, for example, It is the average of those values at each measurement. In the calculation of the membrane exchange rate,
The calculation may be performed with the membrane exchange period being constant, or the period may be changed to determine the optimum membrane exchange rate and the exchange time from the relationship between the membrane exchange rate and the exchange period.
Further, the optimum membrane exchange rate can be set within a specific period, or the optimum membrane exchange rate can be set so that the membrane exchange rate is always constant.

If the reverse osmosis membrane exchange rate setting method or apparatus of claim 1 or 2 is used for membrane exchange, the membrane exchange rate will not be excessive even if the necessary margin is taken into consideration. As the processing means, the consolidation coefficient input means (when the consolidation coefficient is calculated) and the membrane exchange rate calculation means, for example, a program incorporated in a microcomputer can be used.

Although the quality of the permeated water actually obtained is influenced by the operating conditions of the apparatus, there is a certain relationship between the operating conditions and the quality of the permeated water. If the operating condition input means for inputting and the correcting means for comparing the operating condition input by this with the design condition of the fresh water producing apparatus and correcting the measured conductivity corresponding to the difference are actually provided, Even when the operating conditions of No. 1 are different from the design conditions, the calculation accuracy of the membrane exchange rate can be maintained by using these means.

[0009]

[Examples] FIG. 1 shows a schematic configuration of an apparatus capable of carrying out the reverse osmosis membrane exchange rate setting method of the embodiment, and FIG. 2 shows a reverse apparatus as a fresh water producing apparatus in which the present method and apparatus can be used. The structural example of the reverse osmosis membrane unit of an osmosis membrane type seawater desalination apparatus is shown. The configuration of this device will be described with reference to these drawings.

In FIG. 2, the seawater desalination apparatus is composed of an assembly provided with a large number of unit reverse osmosis membranes for converting seawater into permeated water having low conductivity by passing through the reverse osmosis membranes. , A, B2 series of unit reverse osmosis membranes are each configured in two stages, and in the first stage, 1F (F means water supply side) to 65F and 1Br (Br means brine side), respectively. A total of 130 unit reverse osmosis membranes consisting of 65Br to 65Br are made into an assembly of two rows of A series and B series, and in the second stage, 1F '(F' means the water supply side) to 30F 'and 1Br' respectively. A total of 60 unit reverse osmosis membranes consisting of (Br 'means the brine side) to 30Br' are formed as an assembly of two rows of A series and B series.
In the seawater desalination apparatus having such a configuration, in the first stage, seawater is supplied as the supply water whose pressure is increased by a high-pressure pump (not shown) from the direction indicated by arrow a, and the permeated water whose conductivity has decreased from the direction indicated by arrow b. A certain first-stage demineralized water is sent out. Then, the first-stage demineralized water becomes the supply water, and the pressure is increased again to be supplied to the second stage from the arrow C direction, and further desalted in the second stage as the permeated water from the arrow D direction to the second-stage demineralized water. Is sent out. After this second demineralized water is further treated in a device not shown, finally fresh water is obtained. In addition,
In the seawater desalination apparatus of the embodiment, the feed water is directly supplied to the reverse osmosis membrane module on the feed water side (F, F ′ side) in both the first and second stages, but the brine side (Br, Br ′). The side) is supplied with the supply water concentrated in the module.

The reverse osmosis membrane exchange rate setting device used in such a seawater desalination apparatus has the following devices. Figure 1
In the unit reverse osmosis membrane device 1F
65F, 1Br to 65Br and 1F 'to 30F', 1B
Sampling racks 101 and 102 and instrument racks 103 and 104 are provided as conductivity measuring means capable of measuring the conductivity of the passing water that has passed through each of r ′ to 30 Br ′.

The sampling racks 101 and 102 include
Manual valves 101-1 and 102-1 and the like are collectively provided. When measuring the conductivity, the measurer sequentially opens and closes these valves, whereby the unit reverse osmosis membranes 1F, 1Br, etc. of the first and second stages and 1F ′,
The 1st-stage demineralized water and the 2nd-stage demineralized water on the water supply side and the brine side that have passed through these from 1Br ′ etc. are supplied as sample water. However, instead of the manual valves 101-1 and 102-1 and the like, an automatic valve such as a solenoid valve is used to automatically open and close at a predetermined time or sequentially open and close by a human operation to save labor in conductivity measurement. It may be designed. The sample source valves 1F-1 and 1F'-1 and the like on the machine side are normally opened.

A conductivity meter 1 is mounted on the instrument racks 103 and 104.
03a and 104a are provided to measure the conductivity of the demineralized water that has been introduced through the reverse osmosis membranes on the water supply side and the brine side.

On-site control panels 105 and 10 are used as input means.
In this embodiment, the operator inputs the name of the reverse osmosis membrane and each measured conductivity into the personal computer controller 107 described below together with the date. However, the input means may be a device that can automatically input to the personal computer control device 107 from the field operation panels 105 and 106, or the personal computer control device 1
07 CRT 107a display screen and keyboard 107b
A device for inputting by using and may be used.

Further, in the reverse osmosis membrane exchange rate setting device of this embodiment, operating conditions include supply water pressure, demineralized and concentrated concentrated water pressure, demineralized water pressure, supply water flow rate, demineralized water flow rate, water temperature, Operation data such as supply water conductivity, supply water salt concentration,
It is obtained from each measuring device installed in the seawater desalination system. Then, these data are input to the main body of the personal computer control device using the CRT 107a and the keyboard 107b of the personal computer control device 107 which is an example of the operating condition input means. However, a computer or the like provided in the seawater desalination apparatus may be used as the operating condition input means, and the data may be automatically input to the main body of the personal computer control apparatus.

The personal computer controller 107 is a CRT 107.
a, a keyboard 107b, a printer 107c, a processing means and a membrane exchange rate determining means, and in this embodiment, an operating condition correcting means.

The correction means compares the measured and input feed water pressure, concentrated water pressure, demineralized water pressure, feed water flow rate, demineralized water flow rate, water temperature, feed water conductivity and feed water salt concentration with design conditions. If there is a difference, the measured individual conductivity is corrected from the difference and a correction coefficient predetermined for each operating condition. This correction is performed in order to obtain the electric conductivity when the plant is operating under the design conditions when the actual operating conditions are different from the design conditions. This allows a correct evaluation of individual membrane performance. However, such a correction unit may not be provided for a plant that is always operated under conditions close to the design conditions.

The processing means first obtains the maximum value, the minimum value, the average value and the standard deviation as a statistical process from the individual data thus corrected. In this embodiment, CR
Using the T107a and the keyboard 107b, the consolidation coefficient at the beginning of the membrane exchange is set to 1.0, and the consolidation coefficient after 1 to 3 years is set to 0.65, and this numerical value is input to the main body of the control device 107. However, by preliminarily incorporating such conditions into the control device main body, the consolidation coefficient may be calculated from the time when the conductivity is measured, that is, the time when the film is used. In the processing means, for example, the initial salt permeability is Spo, the elapsed time until the measurement is t, and the salt permeability after the time t is S.
When the pt and the film deterioration rate coefficient are Ksp, the film deterioration rate coefficient Ksp is calculated using an empirical formula of Log (Spt / Spo) = Ksp · t ^0.65 . In this case, the salt permeability at the initial stage and after the lapse of time t is obtained from the conductivity measured and corrected according to the operating conditions. By using such a membrane deterioration rate coefficient, it becomes possible to grasp the performance of the membrane and reasonably determine the membrane exchange rate. In addition, at the stage where the elapsed time t is short and the amount of data is small, the numerical value given by the reverse osmosis membrane manufacturer may be used.

In the present embodiment, the membrane exchange rate calculation means assumes that the membrane exchange is performed once a year and is performed at a constant membrane exchange rate every year. The membrane exchange rate is obtained under the condition that the water quality after the membrane exchange predicted in each of the first and second stages does not always exceed a predetermined design value. However, the present means may be capable of calculating the relationship between the membrane exchange rate and the membrane exchange timing that maintains a predetermined water quality. By doing this, it is possible to obtain the optimum membrane exchange timing and membrane exchange rate.

FIG. 3 shows the operation and processing flow for setting the membrane exchange rate using such a reverse osmosis membrane exchange rate setting device. The conductivity of each reverse osmosis membrane (“RO membrane” in the table) is measured once a month and input to the personal computer controller 107 (S
1). Further, the record of the operating conditions detected by the sensors is also input to the same device (S2). At this time, a correction coefficient for correcting the conductivity is automatically calculated and input for each operating condition (S
3). From these, a water quality correction value is calculated for each reverse osmosis membrane to create a water quality correction value table (S4). Part of the raw conductivity data input table and the water quality correction value recording table are shown in Table 1 respectively.
And Table 2 illustrates. This water quality correction includes correction between the water supply side and the brine side where the water quality is different even in the same stage.

Next, in this embodiment, since the membrane is changed once a year, the record is also input to the personal computer control device 107 (S5). Then, the time during which each unit reverse osmosis membrane is operated after the membrane exchange is calculated (S6). From the corrected water quality and operating time of each reverse osmosis membrane, a corrected water quality transition table for the operating time of each series is created (S7). In the actual table, monthly data is prepared for all the films, and a part of them is shown in Table 3.

[Table 1]

[Table 2]

[Table 3]

Based on this corrected water quality transition table, the first stage and the second stage are collectively tabulated and statistical data for each elapsed month after the start of use of the plant are summarized to calculate a consolidation coefficient and a membrane deterioration rate coefficient. From these, it is assumed that the membrane exchange is performed once a year at a constant membrane exchange rate, and the membrane exchange rate is calculated so that the water quality that changes with time does not exceed the design performance. Then, these are summarized in a table and displayed as a water quality table for operating hours (S
8). Table 4 exemplifies a part of such a first stage desalination water concentration transition summary table, and FIG. 4 is a graph display thereof.

[Table 4]

In Table 4, the number of elapsed months indicates the number of months after the reverse osmosis membrane has been replaced, and the data of a group of membranes having the same number of elapsed months is entered every month. Shows only. The membrane degradation rate coefficient is calculated monthly by the water quality obtained by adding three times the standard deviation to the average value of a group of measured and corrected data. Then, in the calculation of the expected performance of the water quality, which is calculated every December with the membrane exchange rate being constant, the average value of the membrane deterioration rate coefficient for December calculated for each month is used.
However, since the amount of data collected is small, the film deterioration rate coefficient given by the manufacturer is used in the calculation of Table 4 for the time being. Also, the consolidation coefficient uses the value recommended by the film manufacturer. In the table, the design performance and new predicted performance columns are
Based on the initially designed and corrected actual measurement values (ppm), the transitions when the membrane is not replaced are shown.
In this case, the guaranteed water quality as the design performance is 400 ppm, and if the performance of the device is as designed, then 36
After a month, it will exceed the guaranteed value. As the new predicted performance when the membrane is not replaced and the predicted performance when the membrane is replaced, as described above, a safe value is used in which the standard deviation is tripled in the average value of the corrected actual measurement values. Based on this, the performance transition is calculated when the membrane is replaced at a fixed rate every year. The expected transition (ppm) at the time of membrane exchange in the right column shows the expected water quality with respect to the number of months elapsed when membrane exchange was performed at a constant membrane exchange rate of 7%, 9% or 18%, respectively. The actual calculation is performed up to 15 years, but Table 4 exemplifies up to 7 February (6 years). The first 7% exchange rate in the right column shows the maximum membrane exchange rate that exceeds the guaranteed value of 400 ppm when the membrane exchange rate is calculated at a pitch of 2%, which is not seen in the table. After 9 years (August), expected performance exceeds 400 ppm. The next 9% exchange rate was calculated in the same way and the lowest value that did not exceed the guaranteed value of 400 ppm was obtained. With this membrane exchange rate, the water quality was closest to 400 ppm after 12 years (April). There is. The exchange rate of 18% at the right end is a freely selectable numerical value, and if the degree of data integration is sufficient, it may coincide with the central column (9% in this case). The numerical values in the exchange rate column of the table indicate the values calculated when the membrane was replaced every 12 months after the start of operation, including the effect of the subsequent membrane replacement. FIG. 4 is a graphical representation of this result. For replacement performance, the replacement rate is 7%
(1 at the time of replacement) and 18% (2 at the time of replacement) are shown.

Table 5 shows an example of a tabulation table of operating conditions input from the operating record. The measured values are corrected based on these operating specifications. 5 and 6 are graphs showing the desalinated water concentration distribution of the unit reverse osmosis membrane in the designated months and the changes in the desalinated water concentration summarized for each stage and series. Table 6 is an example of a reverse osmosis membrane exchange recording table for calculating the operating time of the reverse osmosis membrane.

[Table 5]

[Table 6] The various calculations and processes described above can be efficiently performed by, for example, a commercially available spreadsheet software and an analysis program of BASIC.

With such a reverse osmosis membrane exchange rate setting device, the recommended value of the membrane exchange rate of the manufacturer that has been conventionally used is 25.
It is possible to adopt a membrane exchange rate of 15% or less, while it is ˜30%, and the economical efficiency of the plant is significantly improved. Then, by gradually adding the collected data, the reliability of the performance prediction increases, and the membrane exchange rate can be further reduced. Further, it is possible to grasp the overall performance of the plant and record the membrane exchange at the same time.

Depending on the type of the reverse osmosis membrane, the membrane exchange may be carried out mainly by the amount of water rather than the water quality.
In such a case, the amount of water in each unit reverse osmosis membrane can be detected, and the membrane exchange rate can be determined by the same process based on this. In addition, in the above, when actually performing the membrane replacement, consider that there is a difference in the degree of deterioration of the membrane due to, for example, the influence of microorganisms or other conditions of use, or the characteristics of individual membranes. In the water quality correction value recording table, it is desirable to replace a predetermined number of membranes in order from the one with the largest water quality deterioration.

[0027]

As described above, according to the present invention, an appropriate membrane exchange rate can be set, and the maintenance cost of the seawater desalination apparatus can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a reverse osmosis membrane exchange rate setting device according to an embodiment.

FIG. 2 is an explanatory diagram showing an arrangement of unit reverse osmosis membrane devices of a seawater desalination device to which the above device is applied.

FIG. 3 is a flow chart when the membrane exchange rate is determined by the above apparatus.

FIG. 4 is a graph showing changes in expected concentration of desalinated water.

FIG. 5 is a graph showing a concentration distribution of demineralized water.

FIG. 6 is a graph showing changes in the concentration of demineralized water.

[Explanation of symbols]

1F-65F, 1Br-65Br 1st-stage unit reverse osmosis membrane 1F'-30F ', 1Br'-30Br' 2nd-stage unit reverse osmosis membrane 101,102 Sampling rack (conductivity measuring means) 103,104 Instrument rack (conductivity) Rate measuring means) 105, 106 Operation panel (input means) 107 Control device (processing means, membrane exchange rate calculation means) 107a CRT (input means) 107b Keyboard (input means)

Claims (2)

[Claims] 1. A reverse osmosis membrane exchange rate setting method for use in a fresh water producing apparatus comprising a large number of unit reverse osmosis membranes arranged in parallel or in series as an aggregate, wherein the conductivity of permeated water is set for each unit reverse osmosis membrane. The conductivity and the period of use of the unit reverse osmosis membrane are input to the processing means, and the deterioration rate coefficient of the reverse osmosis membrane is determined by the input data and the consolidation coefficient by which the reverse osmosis membrane is consolidated. Due to the consolidation coefficient and the deterioration rate coefficient, the quality of permeated water predicted as the fresh water producing apparatus does not always exceed a predetermined value, with respect to the total number of reverse osmosis membranes constituting the fresh water producing apparatus. A method for setting a reverse osmosis membrane exchange rate characterized by determining a membrane exchange rate which is a ratio of the number of unit reverse osmosis membranes to be exchanged. 2. A reverse osmosis membrane exchange rate setting device for use in a fresh water producing apparatus, comprising a large number of unit reverse osmosis membranes arranged in parallel or in series and configured as an assembly, wherein the conductivity of permeate of each unit reverse osmosis membrane is adjusted. Reversed by the conductivity measuring means to be measured, the input means for inputting the measured conductivity and the period of use of the unit reverse osmosis membrane to the processing means, and the input data and the consolidation coefficient by which the reverse osmosis membrane is consolidated. The treatment means for determining the deterioration rate coefficient of the osmosis membrane, and the water quality of the permeated water predicted as the fresh water manufacturing apparatus calculated by the consolidation coefficient and the deterioration rate coefficient, so that the water quality does not always exceed a predetermined value. And a membrane exchange rate calculation means for determining a membrane exchange rate which is a ratio of the number of unit reverse osmosis membranes to be exchanged with respect to the total number of reverse osmosis membranes constituting the fresh water producing apparatus. Permeation membrane exchange rate setting device.